Use of activated carbon for separation of ethanol from water

ABSTRACT

An adsorptive separation process for separating ethanol from a feed mixture comprising ethanol and water, which process comprises contacting the feed mixture with an adsorbent comprising activated carbon, selectively adsorbing substantially all of the ethanol to be separated to the substantial exclusion of the water and thereafter recovering high purity ethanol. A desorption step is used to desorb the adsorbed ethanol with the desorbent selected being capable of direct blending into motor fuel.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of our prior copendingapplication Ser. No. 202,048, filed Oct. 30, 1980, now abandonedincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This field of art to which the claimed invention pertains is solid-bedadsorptive separation. More specifically, the claimed invention relatesto a process for the separation of ethanol from a feed mixturecomprising ethanol and water which process employs a solid adsorbentwhich selectively removes the ethanol from the feed mixture.

2. Description of the Prior Art

Diminishing world supplies and availability of crude oil as well assporadic regional shortfalls of gasoline for motor fuel have createdconsiderable incentive for the development and use of alternative fuels.Ethanol is gaining wide popularity as such a fuel, particularly whenmixed with gasoline to form a mixture known as gasohol. Gasohol maycontain up to about 10 volume percent ethanol, without modifications topresently used automobile engines being required, thereby extending thevolume of motor fuel availability by a like percentage.

The primary source of the ethanol used in gasohol is derived primarilyfrom the fermentation of mash, usually from corn. Natural fermentationis able to produce an ethanol-water product mixture containing at themost about 12 vol.% ethanol. It is therefore necessary to concentratethe ethanol by distillation which, of course, requires a great amount ofenergy, and, in fact, the greatest cost in production of ethanol byfermentation is the energy required to separate the ethanol from thewater by distillation. A means of achieving this separation without sucha great expenditure of energy would thus be extremely valuable. One,therefore, might consider the many known adsorptive separation processesknown in the art for possible application to the separation of ethanolfrom water.

For example, it is well-known in the separation art that certaincrystalline aluminosilicates can be used to separate hydrocarbon speciesfrom mixtures thereof. The separation of normal paraffins from branchedchain paraffins, for example, can be accomplished by using a type Azeolite which has pore openings from 3 to about 5 Angstroms. Such aseparation process is disclosed in U.S. Pat. Nos. 2,985,589 and3,201,491. These adsorbents allow a separation based on the physicalsize differences in the molecules by allowing the smaller or normalhydrocarbons to be passed into the cavities within the zeoliticadsorbent, while excluding the larger or branched chain molecules.

U.S. Pat. Nos. 3,265,750 and 3,510,423, for example, disclose processesin which large pore diameter zeolites such as the type X or type Ystructured zeolites can be used to separate olefinic hydrocarbons.

In addition to separating hydrocarbon types, the type X or type Yzeolites have also been employed in processes to separate individualhydrocarbon isomers. In the process described in U.S. Pat. No.3,114,782, for example, a particular zeolite is used as an adsorbent toseparate alkyl-trisubstituted benzene; and in U.S. Pat. No. 3,668,267 aparticular zeolite is used to separate specific alkyl-substitutednaphthalenes. In processes described in U.S. Pat. Nos. 3,558,732,3,686,342 and 3,997,620, adsorbents comprising particular zeolites areused to separate para-xylene from feed mixtures comprising para-xyleneand at least one other xylene isomer by selectively adsorbingpara-xylene over the other xylene isomers. In the last mentionedprocesses the adsorbents used are para-xylene selective; para-xylene isselectively adsorbed and recovered as an extract component while therest of the xylenes and ethylbenzenes are all relatively unadsorbed withrespect to para-xylene and are recovered as raffinate components. Also,in the last mentioned processes the adsorption and desorption may becontinuously carried out in a simulated moving bed countercurrent flowsystem, the operating principles and sequence of which are described inU.S. Pat. No. 2,985,589.

Unfortunately, with the adsorbents of the above processes separation ofethanol from water would be out of the question because all of thoseadsorbents are hydrophilic, i.e. they would be selective for water overthe ethanol. Thus, in using any of these adsorbents it would benecessary to extract the water which is the major component and rejectthe ethanol into the raffinate. Also, there would be the problem of whatcould be used as an effective desorbent. The separation of thedesorbent, if possible, from the ethanol raffinate and water extractwould be considerably more costly than the primary distillation of thealcohol from the water.

In U.S. Pat. No. 2,474,170 mention is made that activated carbon may beemployed as an adsorbent to separate the metabolism products fromfermentation processes including the process producing ethyl-alcohol.This reference suggests one of two means for recovering the adsorbedcomponents; (a) treatment of the adsorbent with steam, or (b) heatingthe adsorbent in vacuo. The first mentioned means would, of course,contaminate the extract stream with water, which would at leastpartially defeat the purpose for the extraction to begin with, and thelatter means would require the costly input of heat and the very costlyproviding of a vacuum.

We have discovered a hydrophobic adsorbent selective for ethanol overwater and a unique means for recovering the ethanol which isparticularly suited for the subsequent use of the extract stream ingasohol.

In brief summary, the present invention is, in one embodiment, a processfor separating ethanol from a feed mixture comprising ethanol and water.The process comprises contacting, at adsorption conditions, the mixturewith an adsorbent comprising activated carbon, selectively adsorbing theethanol to the substantial exclusion of water, and thereafter recoveringhigh purity ethanol by treating the adsorbent with a desorbent materialhaving utility as a motor fuel ingredient, thereby enabling the extractstream to be used directly for motor fuel blending.

In another embodiment the present invention is a process for separatingethanol from a feed mixture comprising ethanol and water which processcomprises contacting at adsorption conditions the mixture with anadsorbent comprising activated carbon which process comprises the stepsof: (a) maintaining net fluid flow through a column of the adsorbent ina single direction, which column contains at least three zones havingseparate operational functions occurring therein and being seriallyinterconnected with the terminal zones of the column connected toprovide a continuous connection of the zones; (b) maintaining anadsorption zone in the column, the zone defined by the adsorbent locatedbetween a feed inlet stream at an upstream boundary of the zone and araffinate outlet stream at a downstream boundary of the zone; (c)maintaining a purification zone immediately upstream from the adsorptionzone, the purification zone defined by the adsorbent located between anextract outlet stream at an upstream boundary of the purification zoneand the feed inlet stream at a downstream boundary of the purificationzone; (d) maintaining a desorption zone immediately upstream from thepurification zone, the desorption zone defined by the adsorbent locatedbetween a desorbent inlet stream at an upstream boundary of the zone andthe extract outlet stream at a downstream boundary of the zone; (e)passing the feed stream into the adsorption zone at adsorptionconditions to effect the selective adsorption of the ethanol by theadsorbent in the adsorption zone and withdrawing a raffinate outletstream from the adsorption zone; (f) passing a desorbent material intothe desorption zone at desorption conditions to effect the displacementof the ethanol from the adsorbent in the desorption zone, the desorbentmaterial having utility as a motor fuel ingredient; (g) withdrawing anextract stream comprising the ethanol and desorbent material from thedesorption zone, the extract stream having the capability of being useddirectly for motor fuel blending; and (h) periodically advancing throughthe column of adsorbent in a downstream direction with respect to fluidflow in the adsorption zone, the feed inlet stream, raffinate outletstream, desorbent inlet stream, and extract outlet stream to effect theshifting of zones through the adsorbent and the production of extractoutlet and raffinate outlet streams.

Other objectives and embodiments of the invention encompass detailsabout feed mixtures, adsorbents, desorbent materials and operatingconditions, all of which are hereinafter disclosed in the followingdiscussion of each of the facets of the present invention.

DESCRIPTION OF THE INVENTION

Activated carbon as used as an adsorbent in the present invention is thecommonly known amorphous form of carbon which is treated to obtain alarge surface area (300 to 2000 m² /g). The large surface area impliesthere exists a highly developed internal pore structure in the activatedcarbon, thus providing the well-known ability to adsorb gases and vaporsand various substances dissolved or dispersed in liquids. Activatedcarbon used for liquid phase operations, such as decolorizing, isnormally a light fluffy powder, while that used for gas phaseoperations, such as vapor adsorption, is usually a hard, dense granularpellet. The former is commonly derived from bones, wood, peat, ligniteand paper mill waste which, to obtain the activated carbon, is reactedwith an inorganic chemical compound to degrade or dehydrate the organicmolecules during carbonization or calcination, while the latter type ofactivated carbon is commonly derived from coconut shells, coal, peat andpetroleum residues which, to obtain the activated carbon, is firstcarbonized and then oxidized with air at low temperature, or steam,carbon dioxide, or flue gas at high temperature.

The adsorbents used in the process of this invention can be betterunderstood by brief reference to certain adsorbent properties which arenecessary to the successful operation of a selective adsorption process.It will be recognized that improvements in any of these adsorbentcharacteristics will result in an improved separation process. Amongsuch characteristics are: adsorptive capacity for some volume of anextract component per volume of adsorbent, the selective adsorptive ofan extract component with respect to a raffinate component and thedesorbent material, sufficiently fast rates of adsorption and desorptionof the extract component to and from the adsorbent; and, in instanceswhere the components of the feed mixture are very reactive, little or nocatalytic activity for undesired reactions such as polymerization andisomerization.

Feed mixtures to be utilized in the process of this invention willcomprise a mixture of ethanol and water. To separate ethanol from a feedmixture containing ethanol and water, the mixture is contacted with theadsorbent and the ethanol is more selectively adsorbed and retained bythe adsorbent while the water is relatively unadsorbed and is removedfrom the interstitial void spaces between the particles of adsorbent andthe surface of the adsorbent. The adsorbent containing the ethanol isreferred to as a "rich" adsorbent--rich in ethanol.

The more selectively adsorbed feed component is commonly referred to asthe extract component of the feed mixture, while the less selectivelyadsorbed component is referred to as the raffinate component. Fluidstreams leaving the adsorbent comprising an extract component andcomprising a raffinate component are referred to, respectively, as theextract stream and the raffinate stream. Thus, the raffinate stream willcontain as a raffinate component the feed mixture component other thanthe selected component and the extract stream will contain the selectedcomponent a the extract component.

Although it is possible by the process of this invention to produce highpurity (98% or greater) ethanol product at high recoveries, it will beappreciated that an extract component is never completely adsorbed bythe adsorbent, nor is a raffinate component completely non-adsorbed bythe adsorbent. Therefore, small amounts of a raffinate component canappear in the extract stream, and, likewise, small amounts of an extractcomponent can appear in the raffinate stream. The extract and raffinatestreams then are further distinguished from each other and from the feedmixture by the ratio of the concentrations of an extract component and aspecific raffinate component, both appearing in the particular stream.For example, the ratio of concentration of the more selectively adsorbedethanol to the concentration of a less selectively adsorbed water willbe highest in the extract stream, next highest in the feed mixture, andlowest in the raffinate stream. Likewise, the ratio of the lessselectively adsorbed water to the more selectively adsorbed ethanol willbe highest in the raffinate stream, next highest in the feed mixture,and the lowest in the extract stream.

The adsorbent can be contained in one or more claims were throughprogrammed flow into and out of the chambers separation of the ethanolis effected. The adsorbent will preferably be contacted with a desorbentmaterial is capable of displacing the adsorbed ethanol from theadsorbent. The resultant extract stream comprising the ethanol anddesorbent material may be subjected to a separation step so as to obtainhigh purity ethanol, however, when the desorbent material is oneordinarily useful for gasoline blending, the ethanol-desorbent mixturecould be used directly for that purpose without a need for theseparation step. Alternatively, the ethanol could be removed from theadsorbent by purging or by increasing the temperature of the adsorbentor by decreasing the pressure of the chamber or vessel containing theadsorbent or by a combination of these means.

The adsorbent may be employed in the form of a dense compact fixed bedwhich is alternatively contacted with the feed mixture and desorbentmaterials. In the simplest embodiment of the invention, the adsorbent isemployed in the form of a single static bed in which case the process isonly semi-continuous. In another embodiment a set of two or more staticbeds may be employed in fixed bed contacting with appropriate valving sothat the feed mixture is passed through one or more adsorbent beds whilethe desorbent materials can be passed through one or more of the otherbeds in the set. The flow of feed mixture and desorbent materials may beeither up or down through the desorbent. Any of the conventionalapparatus employed in static bed fluid-solid contacting may be used.

Countercurrent moving-bed or simulated moving-bed counter-current flowsystems, however, have a much greater separation efficiency than fixedadsorbed bed systems and are therefore preferred for use in ourseparation process. In the moving-bed or simulated moving-bed processesthe adsorption and desorption operations are continuously taking placewhich allows both continuous production of an extract and a raffinatestream and the continual use of feed and desorbent streams. Onepreferred embodiment of this process utilizes what is known in the artas the simulated moving-bed countercurrent flow system. The operatingprinciples and sequence of such a flow system are described in U.S. Pat.No. 2,985,589 incorporated herein by reference. In such a system, it isthe progressive movement of multiple liquid access points down anadsorbent chamber that simulates the upward movement of adsorbentcontained in the chamber. Only four of the access lines are active atany one time; the feed input stream, desorbent inlet stream, raffinateoutlet stream, and extract outlet stream access lines. Coincident withthis simulated upward movement of the solid adsorbent is the movement ofthe liquid occupying the void volume of the packed bed of adsorbent. Sothat countercurrent contact is maintained, a liquid flow down theadsorbent chamber may be provided by a pump. As an active liquid accesspoint moves through a cycle, that is, from the top of the chamber to thebottom, the chamber circulation pump moves through different zones whichrequire different flow rates. A programmed flow controller may beprovided to set and regulate these flow rates.

The active liquid access points effectively divide the adsorbent chamberinto separate zones, each of which has a different function. In thisembodiment of the process, it is generally necessary that three separateoperational zones be present in order for the process to take place,although in some instances an optional fourth zone may be used.

The adsorption zone, zone 1, is defined as the adsorbent located betweenthe feed inlet stream and the raffinate outlet stream. In this zone, thefeed stock contacts the adsorbent, an extract component is adsorbed, anda raffinate stream is withdrawn. Since the general flow through zone 1is from the feed stream which passes into the zone to the raffinatestream which passes out of the zone, the flow in this zone is consideredto be a downstream direction when proceeding from the feed inlet to theraffinate outlet streams.

Immediately upstream with respect to fluid flow in zone 1 is thepurification zone, zone 2. The purification zone is defined as theadsorbent between the extract outlet stream and the feed inlet stream.The basic operations taking place in zone 2 are the displacement fromthe non-selective void volume of the adsorbent of any raffinate materialcarried into zone 2 by the shifting of adsorbent into this zone and thedesorption of any raffinate material adsorbed within the selective porevolume of the adsorbent or adsorbed on the surfaces of the adsorbentparticles. Purification is achieved by passing a portion of extractstream material leaving zone 3 into zone 2 at zone 2's upstreamboundary, the extract outlet stream, to effect the displacement ofraffinate material. The flow of material in zone 2 is in a downstreamdirection from the extract outlet stream to the feed inlet stream.

Immediately upstream of zone 2 with respect to the fluid flowing in zone2 is the desorption zone or zone 3. The desorption zone is defined asthe adsorbent between the desorbent inlet and the extract outlet stream.The function of the desorption zone is to allow a desorbent materialwhich passes into this zone to displace the extract component which wasadsorbed upon the adsorbent during a previous contact with feed in zone1 in a prior cycle of operation. The flow of fluid in zone 3 isessentially in the same direction as that of zones 1 and 2.

In some instances an optional buffer zone, zone 4, may be utilized. Thiszone, defined as the adsorbent between the raffinate outlet stream andthe desorbent inlet stream, if used, is located immediately upstreamwith respect to the fluid flow to zone 3. Zone 4 could be utilized toconserve the amount of desorbent utilized in the desorption step since aportion of the raffinate stream which is removed from zone 1 can bepassed into zone 4 to displace desorbent material present in that zoneout of that zone into the desorption zone. Zone 4 will contain enoughadsorbent so that the raffinate material present in the raffinate streampassing out of zone 1 and into zone 4 can be prevented from passing intozone 3 thereby contaminating extract stream removed from zone 3. In theinstances in which the fourth operational zone is not utilized theraffinate stream passed from zone 1 to zone 4 must be carefullymonitored in order that the flow directly from zone 1 to zone 3 can bestopped when there is an appreciable quantity of raffinate materialpresent in the raffinate stream passing from zone 1 into zone 3 so thatthe extract outlet stream is not contaminated.

A cyclic advancement of the input and output streams through the fixedbed of adsorbent can be accomplished by utilizing a manifold system inwhich the valves in the manifold are operated in a sequential manner toeffect the shifting of the input and output streams thereby allowing aflow of fluid with respect to solid adsorbent in a countercurrentmanner. Another mode of operation which can effect the countercurrentflow of solid adsorbent with respect to fluid involves the use of arotating disc valve in which the input and output streams are connectedto the valve and the lines through which feed input, extract output,desorbent input and raffinate output streams pass are advanced in thesame direction through the adsorbent bed. Both the manifold arrangementand disc valve are known in the art. Specifically, rotary disc valveswhich can be utilized in this operation can be found in U.S. Pat. Nos.3,040,777 and 3,422,848, incorporated herein by reference. Both of theaforementioned patents disclose a rotary type connection valve in whichthe suitable advancement of the various input and output streams fromfixed sources can be achieved without difficulty.

In many instances, one operational zone will contain a much largerquantity of adsorbent than some other operational zone. For instance, insome operations the buffer zone can contain a minor amount of adsorbentas compared to the adsorbent required for the adsorption andpurification zones. It can also be seen that in instances in whichdesorbent is used which can easily desorb extract material from thedesorbent that a relatively small amount of adsorbent will be needed ina desorption zone as compared to the adsorbent needed in the buffer zoneor adsorption zone or purification zone or all of them. Since it is notrequired that the adsorbent be located in a single column, the use ofmultiple chambers or a series of columns is within the scope of theinvention.

It is not necessary that all of the input or output streams besimultaneously used, and in fact, in many instances some of the steamscan be shut off while others effect an input or output of material. Theapparatus which can be utilized to effect the process of this inventioncan also contain a series of individual beds connected by connectingconduits upon which are placed input or output taps to which the variousinput or output streams can be attached and alternately and periodicallyshifted to effect continuous operation. In some instances, theconnecting conduits can be connected to transfer taps which during thenormal operations do not function as a conduit through which materialpasses into or out of the process.

References can be made to D. B. Broughton U.S. Pat. No. 2,985,589, andto a paper entitled, "Continuous Adsorptive Processing--A New SeparationTechnique" by D. B. Broughton presented at the 34th Annual Meeting ofthe Society of Chemical Engineers at Tokyo, Japan, on Apr. 2, 1969,incorporated herein by reference, for further explanation of thesimulated moving-bed countercurrent process flow scheme.

Adsorption and desorption conditions for adsorptive separation processescan generally be either in the liquid or vapor phase or both. Preferredadsorption conditions for the process of this invention will includetemperatures within the range of from about 20° C. to about 230° C. andwill include pressures in the range from about atmospheric to about 500psig. Pressures higher than about 500 psig do not appear to effect theselectivity to a measurable amount and additionally would increase thecost of the process. Desorption conditions for the process of theinvention shall generally include the same range of temperatures andpressures as described for adsorption operations. The desorption of theselectively adsorbed ethanol could also be effected at subatmosphericpressures or elevated temperatures or both or by vacuum purging of theadsorbent to remove the ethanol as suggested in the aforementioned U.S.Pat. No. 2,474,170, but this process is not directed to these desorptionmethods. The desorbent material relied upon must be judiciously selectedto satisfy several criteria. First, the desorbent material must displacethe adsorbed ethanol from the adsorbent with reasonable mass flow rateswithout itself being so strongly adsorbed as to unduly prevent theethanol from displacing the desorbent material in a following adsorptioncycle. Secondly, desorbent materials must be compatible with theparticular adsorbent and the particular feed mixture. More specifically,they must not reduce or destroy the critical selectivity of theadsorbent for the ethanol with respect to water. Finally, and in furthercontradistinction to the prior art, desorbent materials to be used inthe process of this invention must additionally be substances which arethemselves useful for motor fuel blending. Preferred desorbent materialfor use in the process of this invention may be one or a mixture of thecommon ingredients of gasoline, particularly aromatic and other highoctane liquid hydrocarbons (at standard conditions) such as isooctane.

A dynamic testing apparatus may be employed to test various adsorbentswith a particular feed mixture and desorbent material to measure theadsorbent characteristics of adsorptive capacity, selectivity andexchange rate. The apparatus consists of an adsorbent chamber ofapproximately 70 cc volume having inlet and outlet portions at oppositeends of the chamber. The chamber is contained within a temperaturecontrol means and, in addition, pressure control equipment is used tooperate the chamber at a constant predetermined pressure.Chromatographic analysis equipment can be attached to the outlet line ofthe chamber and used to detect qualitatively or determine quantitativelyone or more components in the effluent stream leaving the adsorbentchamber. A pulse test, performed using this apparatus and the followinggeneral procedure, is used to determine selectivities and other data forvarious adsorbent systems. The adsorbent is filled to equilibrium with aparticular desorbent material by passing the desorbent material throughthe adsorbent chamber. At a convenient time, a pulse of feed containingknown concentrations of a non-adsorbed tracer and of an ethanol-watermixture, all diluted in desorbent, is injected for a duration of severalminutes. Desorbent flow is resumed, and the tracer and the feedcomponents are eluted as in a liquid-solid chromatographic operation.The effluent is collected in fractions and analyzed usingchromatographic equipment and traces of the envelopes of correspondingcomponent peaks developed.

From information derived from the test, adsorbent performance can berated in terms of retention volume for an extract or a raffinatecomponent, selectivity for one component with respect to the other, andthe rate of desorption of an extract component by the desorbent. Theretention volume of an extract or a raffinate component may becharacterized by the distance between the center of the peak envelope ofan extract or a raffinate component and the peak envelope of the tracercomponent or some other known reference point. It is expressed in termsof the volume in cubic centimeters of desorbent pumped during this timeinterval represented by the distance beween the peak envelopes.Selectivity, (B), for an extract component with respect to a raffinatecomponent may be characterized by the ratio of the distance between thecenter of the extract component peak envelope and the tracer peakenvelope (or other reference point) to the corresponding distance thecenter of the raffinate component peak envelope and the tracer peakenvelope. The rate of exchange of an extract component with thedesorbent can generally be characterized by the width of the peakenvelopes at half intensity. The narrower the peak width the faster thedesorption rate.

Selectivity, (B), with regard to two given components, is equal to thequotient obtained by dividing the respective retention volumes of suchcomponents. Where selectivity of two components approaches 1.0 there isno preferential adsorption of one component by the adsorbent withrespect to the other; they are both adsorbed (or non-adsorbed) to aboutthe same degree with respect to each other. As the (B) becomes less thanor greater than 1.0 there is a preferential adsorption by the adsorbentfor one component with respect to the other. When comparing theselectivity by the adsorbent of one component C over component D, a (B)larger than 1.0 indicates preferential adsorption of component C withinthe adsorbent. A (B) less than 1.0 would indicate that component D ispreferentially adsorbed leaving an unadsorbed phase richer in componentC and an adsorbed phase richer in component D. Ideally, desorbentmaterials should have a selectivity equal to about1 or slightly lessthan 1 with respect to all extract components so that all of the extractcomponents can be desorbed as a class with reasonable flow rates ofdesorbent material and so that extract components can displace desorbentmaterial in a subsequent adsorption step. While separation of an extractcomponent from a raffinate component is theoretically possible when theselectivity of the adsorbent for the extract component with respect tothe raffinate component is greatr than 1.0, it is preferred that suchselectivity be greater than 2.0. Like relative volatility, the higherthe selectivity the easier the separation is to perform. Higherselectivities permit a smaller amount of adsorbent to be used. The rateof exchange relates directly to the amount of desorbent material thatmust be employed in the process to recover the extract component fromthe adsorbent; faster rates of exchange reduce the amount of desorbentmaterial needed to remove the extract component and therefore permit areduction in the operating cost of the process. With faster rates ofexchange, less desorbent material has to be pumped through the processand separated from the extract stream for reuse in the process.

It is also necessary that the adsorbent possess little or no catalyticactivity toward any reaction such as polymerization or isomerization ofany of the feed components. Such activity might effect adsorbentcapacity or selectivity or product yields, or all of these, but in theadsorptive separation of ethanol from water with activated carbonadsorbent, this is generally not a problem.

To further evaluate promising adsorbent systems and to translate thistype of data into a practical separation process, actual testing of thebest system in a continuous countercurrent liquid-solid contactingdevice would be ideal. The general operating principles of such a devicehave been previously described and are found to Broughton U.S. Pat. No.2,985,589 and a specific laboratory-size apparatus utilizing theseprinciples is described in deRosset et al U.S. Pat. No. 3,706,812. Theequipment comprises multiple adsorbent beds with a number of accesslines attached to distributors within the beds and terminating at arotary distributing valve. At a given valve position, feed and desorbentare being introduced through two of the lines and raffinate and extractare withdrawn through two more. All remaining access lines are inactiveand when the position of the distributing valve is advaned by one index,all active positions will be advanced by one bed. This simulates acondition in which the adsorbent physically moves in a directioncountercurrent to the liquid flow. Additional details on adsorbenttesting and evaluation may be found in the paper "Separation of C₈Aromatics by Adsorption" by A. J. deRosset, R. W. Neuzil, A. J. Korous,and D. H. Rosback presented at the American Chemical Society, LosAngeles, Calif., Mar. 28, to Apr. 2, 1971. All of the above referencesare incorporated herein by reference.

ILLUSTRATIVE EXAMPLES AND DESCRIPTION OF THE DRAWINGS

The following examples are of pulse test results obtained from the abovedescribed pulse test apparatus. In all cases the adsorbent column wasstraight, upflow, with capillary controlled pressure. Feed pulses were15 ml each and comprised a 50:50 mixture of ethanol and water. The flowwas down through the column at a rate of 1.1 ml/min. The adsorbentchamber was packed with adsorbent comprising activated carbon obtainedfrom the Calgon Corporation, a subsidiary of Merck and Company, Inc. Theadsorbent comprised hard granules of from 20 to 48 mesh size. Thedesorbents selected were those capable of direct blending into motorfuel, i.e. high octane hydrocarbons, liquid at standard temperature andconditions.

EXAMPLE 1

In this example, toluene was the desorbent, the temperature was 80° C.and the pressure was sufficient to maintain liquid phase, except twophases existed during the time between effluent volumes of about 10 mlto about 75 ml. The results are shown in FIG. 1 of the drawings. FIG. 1shows an essentially complete separation of the ethanol and water over asubstantial portion of the ethanol elution curve.

EXAMPLE 2

In this example, the desorbent was a 15:85 toluene:isooctane blend,which may be considered a gasoline, and, of course, which would be idealfor motor fuel blending. The temperature was 80° C. and the pressure wassufficient to maintain liquid phase, except two phases existed duringthe time between effluent volumes of about 10 ml to about 60 ml. Theresults are shown in FIG. 2 of the drawings. FIG. 2 also shows anessentially complete separation of the ethanol and water over asubstantial portion of the last part of the ethanol elution curve aswell as a very minor amount of water contamination or "tailing" overalmost all of the preceding part of that curve. The present invention isthus capable of yielding gasohol directly as an extract stream andcontaining essentially anhydrous ethanol.

We claim as our invention:
 1. A process for separating ethanol from afeed mixture comprising ethanol and water and for producing a motor fuelblend, which process comprises contacting said mixture at adsorptionconditions with an adsorbent comprising activated carbon, selectivelyadsorbing said ethanol in said adsorbent to the substantial exclusion ofwater, contacting the adsorbent containing the adsorbed ethanol with adesorbent material comprising a high octane hydrocarbon boiling in thegasoline range to desorb said ethanol from the adsorbent, and removingfrom said adsorbent and recovering as said motor fuel blend theresultant mixture of ethanol and desorbent material.
 2. The process ofclaim 1 further characterized in that said desorbent material comprisesisooctane.
 3. The process of claim 1 further characterized in that saidadsorption conditions include a temperature within the range of fromabout 20° C. to about 230° C. and at a pressure within the range of fromabout atmospheric to about 500 psig.
 4. The process of claim 1 whichfurther comprises the steps of:(a) maintaining net fluid flow through acolumn of said adsorbent in a single direction, which column contains atleast three zones having separate operational functions occurringtherein and being serially interconnected with the terminal zones ofsaid column connected to provide a continuous connection of said zones;(b) maintaining an adsorption zone in said column, said zone defined bythe adsorbent located between a feed inlet stream at an upstreamboundary of said zone and a raffinate oulet stream at a downstreamboundary of said zone; (c) maintaining a purification zone immediatelyupstream from said adsorption zone, said purification zone defined bythe adsorbent located between an extract outlet stream at an upstreamboundary of said purification zone and said feed inlet stream at adownstream boundary of said purification zone; (d) maintaining adesorption zone immediately upstream from said purification zone, saiddesorption zone defined by the adsorbent located between a desorbentinlet stream at an upstream boundary of said zone and said extractoutlet stream at a downstream boundary of said zone; (e) passing saidfeed stream into said adsorption zone at adsorption conditions to effectthe selective adsorption of said ethanol by said adsorption in saidadsorption zone and withdrawing a raffinate outlet stream from saidadsorption zone; (f) passing a desorbent material into said desorptionzone at desorption conditions to effect the displacement of said ethanolfrom the adsorbent in said desorption zone, said desorbent materialhaving utility as a motor fuel ingredient; (g) withdrawing an extractstream comprising said ethanol and desorbent material from saiddesorption zone, said extent stream having the capability of being useddirectly for motor fuel blending; (h) periodically advancing throughsaid column of adsorbent in a downstream direction with respect to fluidflow in said adsorption zone the feed inlet stream, raffinate outletstream, desorbent inlet stream, and extract outlet stream to effect theshifting of zones through said adsorbent and the production of extractoutlet and raffinate outlet streams.
 5. The process as described inclaim 4 further characterized in that said desorbent material comprisesisooctane.
 6. The process of claim 4 further characterized in that itincludes the step of maintaining a buffer zone immediately upstream fromsaid desorption zone, said buffer zone defined as the adsorbent locatedbetween the desorbent input stream at a downstream boundary of saidbuffer zone and a raffinate output stream at an upstream boundary ofsaid buffer zone.
 7. The process of claim 4 further characterized inthat said adsorption conditions and desorption conditions include atemperature within the range of from about 20° C. to about 230° C. and apressure within the range of from about atmospheric to about 500 psig.